At the present time, manufacturers who utilize large presses and dies, such as of the type used for forming large sheet metal body parts for automobiles, have attempted to reduce the press size by replacing conventional low-pressure gas springs (typically air springs) with higher pressure springs which are typically filed with nitrogen. This desire to utilize high-pressure gas springs is obviously predicated on the fact that such springs can be of significantly smaller size while still providing a large force-absorbing capacity due to the high internal gas pressure which exists in the spring. These high-pressure springs, however, introduce serious concerns with respect to the safety of such devices and specifically the safety of operating personnel. This is important both during operation of the spring due to the pressure buildup therein during application of impact forces thereto, and also when handling of the spring such as during installation, maintenance or removal. Most known high-pressure springs do not contain control valves for providing safety against pressure overload, and at the same time providing convenient and safe procedures for discharging high-pressure fluid from the spring. Most manufacturers of such springs merely provide the spring with a one-way check valve which permits filling of the spring with a high-pressure gas such as nitrogen, and this check valve must then be manually held in an open position to permit relief of pressure from the spring when depressurization is desired. Having to perform such step is clearly undesirable when handling or maintaining of the spring unit is desired.
Accordingly, this invention relates to a high-pressure gas spring, specifically a nitrogen spring, and in particular to an improved spring having a valve arrangement which functions as a combined check and exhaust valve for permitting filling of the spring with a high-pressure gas, and for readily permitting depressurization of the gas spring substantially to atmospheric pressure in a safe and convenient manner. The valve arrangement additionally functions as a pressure release valve in that it will release excessive pressure from the gas spring in excess of a predetermined magnitude.
In the improved gas spring of the present invention, the valve arrangement employs a control piston which is slidably supported within a bore formed in the air spring housing. The control piston has an internal bore formed therein, and a one-way check valve is positioned therein. One end of this internal bore communicates with the outer end of the housing bore, which in turn communicates with a source of high-pressure gas. The other end of the internal bore communicates with the pressure chamber of the air spring. The high-pressure external gas source is capable of opening the one-way check valve for pressurizing the internal spring chamber, and for supplying makeup pressure in the chamber if a pressure loss occurs. An intermediate discharge passage extends from the pressure chamber to the inner end of the housing bore, and a valve element such as a ball is disposed within this inner end for closing off the intermediate discharge passage. A external discharge passage communicates between the inner end of the housing bore and a discharge reservoir (such as the atmosphere) which is at atmospheric pressure, this external discharge passage being of smaller cross section than the intermediate discharge passage. The source pressure is continuously supplied to the outer end of the housing bore and acts against the control piston for urging the latter towards the inner end, whereby the control piston maintains the valve element in a seated closed position so as to isolate the intermediate discharge passage from the housing bore. In the event of a pressure increase within the spring chamber in excess of a predetermined magnitude, than this is sufficient to urge the valve element and the piston into an open position and, since the external discharge passage is of a smaller cross section and hence effectively acts as a flow restriction, some of the high pressure gas accumulates within the inner end of the housing bore and acts on the control piston so as to move same away from the valve element and maintain the latter in its open position until the pressure in the spring chamber falls below the source pressure, at which time the source pressure moves the control piston back into its closed position.
With the arrangement of the present invention, as explained above, when it is desired to discharge the high-pressure gas from the air spring, such as for maintenance purposes, then the source pressure to the outer end of the housing bore is relieved so as to be substantially atmospheric. The higher pressure in the spring chamber then acts through the intermediate discharge passage and moves the valve element into an open position, whereupon the higher pressure then acts on the adjacent end of the control piston so as to move it away from the valve element so that the latter remains unrestricted in its open position. The high pressure hence then freely flows through the external discharge opening to the atmosphere until the pressure in the pressure chamber is substantially at atmospheric. When repressurization of the spring unit is desired, then a valve in the main supply line is opened so that pressure fluid is again supplied from the source to the outer end of the bore, which in turn moves the control piston against the valve element so as to seat it and hence close off the intermediate discharge passage from the external discharge passage.
The arrangement of the present invention hence provides a convenient and safe operation. Further, the valve arrangement is preferably integrated directly into the head plate of the spring housing so as to ensure that the spring is properly connected since the discharge valve is integrated with the one-way check valve used for controlling pressurization of the cylinder. This hence ensures that the spring unit cannot be improperly utilized and pressurized without ensuring the presence of the discharge control valve.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.